Control system



F. MOHLER CONTROL SYSTEM Nov. 25, 1941.

Filed Aug. 11, 1938 4. Shegts-Sheet 1 Invgntor: Francls Moh ler b 444,".JMAM y His Attorney Nov. 25, 1941. F. MOHLER 2,264,096

CONTROL SYSTEM Filed Aug. 11, 1958 -4 Sheets-Sheet 2 Inventcir:

Francis Mohler',

b9 dunZaM l Attoa "neg.

Nov. 25', 1941. F, MOHLER I 2,254,096

CONTROL SYSTEM Filed Aug. 11, 1958 4 Sheets-Sheet":

Inventor: Francis Mohler,

Nov. 25, 1941. F, HLER 2,264,096,

CONTROL SYSTEM Filed Aug. 11, 1938- 4 Sheets-Sheet 4 AMPLIFIER.

wens/1cm [28 159 CONTROL- AMPLIFIER.

I4 INCRENENT CONTROL.

Inventbr: Francis Mghler,

His Attorney.

Patented Nov. 25, 1941 iii? STATE 2,284,696 CONTROL SYSTEM New YorkApplication August 11, 1938, Serial No. 224,215

7 Claims.

This invention relates to control systems, more particularly to systemsfor controlling apparatus having an element for performing an operationon a length of material under tension, and it has for an object theprovision of a simple, reliable, and improved system of this character.

This application is a continuation-in-part of earlier filed applicationSer. No. 116,656, filed December 18, 1936, and assigned to the sameassignee.

More specifically the invention relates to rolling mill apparatus andthe like having means for reducing the gauge or thicknessof a length ofmaterial and an element for maintaining the material under tension whileits gauge is, being reduced, and a more specific object of the inventionis the provision of improved means for maintaining the gauge of theworked material substantially constant.

In the practice of rolling cold strip material for example, it is highlydesirable to maintain a constant thickness of the rolled strip as nearlyas possible or, in other words, constant gauge is of extreme importance.The trade is becoming very rigid in the allowable tolerances orvariations in gauge. Even with the present precision mills which areequipped with very accurate continuous gauges for measuring the stripthickness at all times, all of the sheets must be sorted and a fairlyhigh percentage is either thicker or thinner than the allowed tolerance.

These mills are equipped with screw-down mechanism for raising andlowering the top rolls and are equipped with tension devices formaintaining substantially constant tension in the strip as it is woundup on drums or reels after emerging from the mill. Some of the mills areof the continuous type utilizing a plurality of stands followed by areel, and some are of the reversing type utilizing a reel on either sideof the mill for winding up and unwinding the strip respectively, andvice versa. The type of'mill, however, is immaterial, since theinvention is applicable to all types. 7

In carrying the invention into effect in one form thereof, means areprovided for responding to variations in the gauge of material beingworked under tension to vary the tension so as to maintain the gaugesubstantially constant. More specifically, as applied to apparatushaving an element for reducing the gauge of a length of material and adevice for tensioning the material, a dynamo electric machine ismechanically coupled to the tensioning device, and a current regulatoris provided for maintaining the current of the dynamo-electric machinesubstantially constant at a set value'together with means responsive tovariations in the gauge of the Worked material for varying the settingof the regulator thereby to maintain the gauge of the material withinthe predetermined tolerance.

In the case of a rolling mill having screwdowns for varying the openingbetween the rolls, means are also provided for controlling thescrew-down mechanism as well as the tension varying means in response tovariations in the gauge of the worked material.

In illustrating the invention in one form thereof, it is illustrated asembodied in a control system for a rolling mill having a pair of rollsfor reducing the gauge of a strip of material, a take up reel, anddriving means for the reel so controlled as to maintain the strip undertension between the rolls and the reel. For a better and more completeunderstanding of the invention, reference should now be had to thefollowing specification and to the accompanying drawings in which Fig. 1is a simple diagrammatical sketch of an embodiment of the invention,Figs. 2, 3, 4 and 5 modifications and Fig. 6 is a detail of theapparatus of Fig.5. I 7

Referring now to the drawings, the thickness of a length of material H]is being reduced by suitable means illustrated as comprising a pair ofrolls H. Rolls H are driven by any suitable driving means such, forexample, as an electric motor (not shown). The length of material I!) isdelivered from the rolls ii in the direction of the arrow and iswoundupon a reel l2 driven by suitable means illustrated as a directcurrent electric motor l3. 1 I

Motor I3 is supplied from a pair of buses H! which are connected to asuitablesource when a switch I5 is moved to its closed position. Asshown, motor I3 is provided with a field winding I6 which is alsoconnected to the bus l4. Suitable starting means are provided forconnecting the motor l3 to the source and for accelerating the motor tofull speed. Motor starters used in actual practice are often quitecomplicated. They may be of the rheostatic type with a number ofsections of resistance and a plurality of accelerating contactors forshort circuiting the resistance sections, or they may be of theadjustable voltage type, in which case the voltage of a generator iscontrolled so as tostart and stop the reel motoix' However, since thespecific structure of the starting means constitutes no' part of thepresentinvention, it is illustrated simply as comprising anelectromagneticcontactor l1 and a switching device, preferably amanually operated pushbutton type switch I 8, for controlling itsenergization. For the purpose of maintaining the tension in the stripbetween the rolls II and the reel l2 substantially constant at apredetermined value, means illustrated as a constant current regulator13 are provided for controlling the input to the reel motor l3. Since itis desirable to maintain the strip speed substantially constant it isnecessary for the speed of the motor l3 to decrease as the diameter ofthe coiled strip increases, in order to maintain the strip tensionbetween the mill rolls and the reels substantially constant at constantstrip speed, it is necessary gradually to increase the excitation of themotor l3 so as to maintain the armature current constant. This isaccomplished by the regulator l9. Although regulator l9 may be of anysuitable type it is shown as a vibratory contact type regulator.Briefly, regulator I9 comprises stationary contact and a movable contact2| arranged for alternately short circuiting and removing the shortcircuit from a resistance 22 included in the field circuit of reel motorI3. A core member 23 is pivotally connected to the arm which carries themovable contact 2| and is arranged within the turns of a solenoid 24which in turn is connected so as to be responsive to the current flowingin the armature circuit of reel motor I3. A spring 25 is attached to themovable contact arm so that its pull opposes the pull of the solenoid onthe core. A second coil 26, referred to as a bias winding, is alsoprovided and arranged to act on the core 23. The operation of theregulator is briefly as follows: With the machine l3 operating as amotor, an increase in the armature current of the motor I3 above thepredetermined value causes the contacts 2 I, 20 to close against thetension of the spring 25 and thereby to short circuit the resistance 22.This increases the excitation of the motor l3 and causes its speed todecrease until the armature current becomes less than the predeterminedvalue at which time the pull of the spring 25 overpowers the pull of thesolenoid and separates the contacts 20, 2| to remove the short circuitabout resistance 22. Reinsertion of the resistance 22 in the fieldcircuit of motor I3 decreases the excitation of the motor and causes itsspeed and armature current to increase. The reel motor armature currentcontinues to increase until it exceeds the predetermined value and againcauses the contacts 20, 2| to close and short circuit the resistance 22.The foregoing operation is repeated at a very rapid rate and thus theregulator tends to vibrate to hold a fixed or constant current in thereel motor armature. A tension adjusting rheostat 211 is included in thecircuit of the current winding. If this rheostat is adjusted to increasethe resistance in series with the winding, more current in the reelmotor armature will be necessary to obtain the required current in. thecurrent winding and therefore the actual current maintained in the reelmotor armature can be increased and decreased by varying the resistancein series with the current winding. For all values of tension, however,the current in the current winding remains at a fixed value.

The purpose of the bias Winding 26 is to provide for changing thesetting of the regulator a fixed percentage of the tension beingmaintained for a predetermined increment adjustment of a controllingrheostat 28. As shown, this controlling rheostat 28 is included incircuit with the bias winding 23 across the buses l4. Winding 26 iswound so that it assists the winding 23 in opposing the pull of thespring 25. Since the pull of the two coils is in the same direction, thepull required from the current winding 23 is decreased by the amount ofthe pull supplied by the bias winding. Thus, if the bias windingsupplied 10% of the pull, only of the pull will a be required from thecurrent winding in order to balance the spring and, in turn, only 90% ofthe current will be required through the reel motor armature to producethis 90% pull. This is true irrespective of the actual value of thetension for which the tension adjusting rheostat 21 is set because, asstated in the foregoing, the current in the current winding remainsfixed at a substantially constant value, irrespective of the tensionbeing maintained. Thus if the tension adjusting rheostats 21 is set for20,000 lbs. tension, and the bias winding supplies 10% of the pull, theactual tension maintained by the regulator will be 18,000 lbs. On theother hand, if the tension adjusting rheostat is set to hold 10,000 lbs.tension, and 10% of the pull on the regulator is supplied by the biaswinding, the actual tension maintained will be 9,000 lbs.

If the control rheostat 28 is sufiicient to vary the pull of biaswinding 26 from practically zero to a substantial value such, forexample, as 50% of the pull required for the regulator, equal incrementadjustment of this rheostat will always represent the same percentagechange of the tension being maintained, irrespective of the setting ofthe tension adjusting rheostat. This feature is desirable because if thestrip is thick and a high tension is being maintained, the incrementadjustment of the tension should also be relatively high as comparedwith the case when the strip is thin and relatively low tensions arebeing maintained.

For the purpose of continuously measuring and indicating the thicknessof the material 10, a suitable gauge 29 is provided. Although severaltypes of gauges and other devices satisfactory for this purpose areavailable on the market, it is preferred to employ a variable air gaptransformer type auge. This type of gauge has a pair of contact rolls30, one above and one below the strip. One of these rolls, preferablythe lower roll, is fixedly mounted, and the other roll is mounted formovement with respect to the first roll in response to changes in thegauge of the strip. These rolls press on the strip at all times, and themovement of one with respect to the other is a measurement of variationsin the thickness of the strip. This movement is transmitted to themovable magnetic vane member 3| of an air gap transformer type gaugehead and, by means of a power unit which includes the necessaryrectifying means 32, an indication of the strip thickness is given on amicroammeter 33 which is calibrated in any convenient unit of stripthickness. This type of gauge is well known to the trade, and since itsspecific internal structural details constitute no part of the presentinvention, a more detailed description is omitted.

The electric gauge indicating instrument 33 is preferably equipped witha zero-center movable contact member 34 and two stationary contacts 35and 36. In practice, these two stationary contacts preferably take theform of mercury cup contacts, the positions of which are adjustable withrespect to the central position of the movable contact member 34. Themovable contact member makes contact with the mercury cup on either sideof the zero position and this circuit closing feature is utilized foractuating the control. The gauge is provided with means for initialadjustment so that the movable contact member 34 will be in the zeroposition when the contact rolls 30 are separated a distance equal to thedesired thickness of the strip. Oversize calibrations are on one side ofthe zero position, preferably the right side, and the tundersizecalibrations are on the left side. 7 Thus, if the strip is running atthe correct gauge, the instrument will indicate zero, but if it runsoversize, the movable contact member will swing to the right inproportion to the amount of the oversize, and conversely, if the stripis running undersize, the movable contact member will swing to the left.The mercury cup contacts can be adjusted in position so that they maycontact with the movable contact member at any desired point. In otherwords, if the total scale deflection to the right represents .005 inchthe mercury cup can be adjusted so that it will make contact when theinstrument indicates .005 inch, or any other desired point such as .002inch. Thus the setting of the mercury cup depends upon the tolerancewhich is to be allowed.

Various mechanisms are available for operating the screws so as to raiseand lower the top rolls. For the purpose of illustration, a simple screwgearing 31 and a direct-current motor 38 for driving the screw areindicated in the drawings.

In this specification the term increment is to be understood as thelength of time, or amount that the screws are raised or lowered or, whenreferring to tension, increment is to be understood as the length oftime or amount the tension is increased or decreased upon each automaticadjustment.

When an indication for correction is given, a second correction shouldnot be made until the effect of the first correction is measured. Thetime required for the correction to be measured depends upon thedistance between the mill rolls and the gauge as well as the timerequired for making the adjustment. Since the distance between the gaugeand the rolls remains fixed, this part of the interval always representsa constant length of strip. That part of the interval which is dependentupon the time required to make the increment adjustment is variable interms of the length of strip. Therefore, if the increment adjustmentrequires .25 second irrespective of the speed of the mill, more stripwill pass through the mill when operating at maximum strip speed thanwhen operating at minimum strip speed. Thus, if the intervals aremeasured as a function of length of strip, the length which passesthrough the mill during the longest increment adjustment and at themaximum speed must be taken into account.

For determining the intervals, a limit switch 39 is provided. This limitswitch is connected either directly or through gearing to the mill rollsin such a manner that one revolution of the limit switch represents thelength of strip which must pass through the mill between successiveincrement adjustments. Relay means 40 controlled by the gauge contacts34, 35, 36 serve to control a pilot motor 4! which rotates the movablecontact arm 28a. of the rheostat 28 in the circuit of the biasing coil26 of the tension regulator. This relay apparatus comprises a switchingdevice 42 and its timing device 43, for controlling the rotation of themotor 4| in such a direction as to increase the tension setting of theregulator, and

a switching device 44 and its timing device for effecting rotation ofthe motor 4| in the opposite direction to decrease the tension settingof the regulator. Switching devices 42 and 44 are illustrated aselectromagnetic contactors, and timing devices 43 and 45 are illustratedas inductive time delay relays, or, magnetic timing type relays. Theserelays have means for adjusting the time interval in their operation.

Similar relay apparatus 46 is provided for controlling the energizationand direction of rotation of the screw-down motor 38. As shown,apparatus 46 comprises an electromagnetic contactor 41 and its timingrelay 48 for effecting rotation of the screw-down motor 33 in adirection to increase the opening between the mill rolls H and anelectromagnetic contactor 49 and its timing relay 59 for effectingoperation of the screwdown motor 38 in a direction to lower the top rolland thereby to decrease the opening between the mill rolls.

Means, illustrated as comprising limit switches 5!, 52, and 53, andcorresponding selector switches 54, 55, and 56, are provided formaintaining the screw actuating mechanism inactive in response tovariations in the gauge of the material until the tension regulatingmechanism has varied the tension a preselectable percentage of the valuethe tension regulator is set to hold.

With the foregoing understanding of the elements and their organizationin thecomplete control system, the operation of the system itseif willreadily be understood from the following detailed description: Thesystem is placed in condition for operation by closing the line switchl5 to energize the buses Hi. This completes an energizing circuit forthe timing relays d3, 65, 28 and 58. The energizing circuit for timingrelay i3 is traced from the upper bus it through the upper contact ofcontactor 42, through coil of relay 3 to the lower bus M. Similarenergizing circuits for timing relays Q5, 48 and 53 are obvious. Inresponse to energization. timing .relays 53, 4.5, 48 and 5t close theircontacts.

The reel motor I3 is started by depressing the start button switch !8 toclose its contacts and thereby to complete an energizing circuit for theoperating coil of starting contactor H. In response to energization,contactor H closes its upper main contacts to complete a supply circuitfor the armature of reel motor l3 that .is traced from the upper bus Id,through upper contacts of contactor ll, armature of motor I3 to lowerbus i=1. As a result, motor 53 is energized and the regulator l9functions in the manner described in the foregoing to'maintain constantcurrent input to the armature of reel motor l3. Switch El is closed toplace the system in condition for automatic operation.

As long as the gauge of the strip remains within the predeterminedtolerances for which the gauge 29 is set, the bridge circuit in the headof the gauge 29 remains balanced and no voltage is supplied to thecontact-making microammeter 33. However, if the strip H3 should begin torun oversize, the movable contact member 3 3 will swing to the right andmake contact with the stationary contact 35 partially to complete anenergizing circuit for the contactor 42. This circuit is completed whenthe conducting segment 39a of the limit switch makes contact with thebrush 39b. The circuit is traced from the upper bus I4 through the limitswitch switch 51, second contact, from the top of contactor ll,conductors '58 and '59, movable contact member 34, stationary contactmember 36, conductor 69,

operating coil of contactor 421, and thence by conductor 6| to the lowerbus l4. Contactor 42 closes in response to energization, and its closingcompletes a circuit through ,the armature oi thermostat motor 4| and itsseries split field winding Me. This circuit is traced from the upper busI 4 through conductor 62, lower contact of contactor 42, split fieldwinding 41a, armature of motor 4i to the lower bus 14. Motor 4|thereupon rotates the movable contact arm 28a. in such a direction as toincrease the tension setting of the tension regulator 19. In closing,contactor 42 completes a holding circuit for itself independently of thelimit switch 39 so that the contactor remains closed after theconducting portion 39a. of the limit switch has rotated out of contactwith the brush 39b. is traced from the upper bus 14 through conductor62, intermediate contact of contactor 42v contacts of time delay relay43, conductor 63, conductors 58 and 59, contacts 34 and 35, conductor69, operating coil of contactor 42 and conductor 6| to the lower bus 14.Contactor 42 in closing interrupts the energizing circuit for the timedelay relay 43 and after an interval of time determined by theadjustment of the time delay relay 43, this relay opens its contacts tointerrupt the holding circuit for the contactor 42 which thereupon opensits lower contacts to interrupt the armature circuit of the rheostatmotor 4|. Movable contact arm 28a of the rheostat comes to rest afterhaving increased the resistance in circuit with the bias winding of theregulator. rent must flow in the armature circuit of the reel motor inorder to produce suflficient current in the current winding 23 of theregulator to balance the pull of the spring 25, This increased armaturecurrentralso increases the tension in the strip between the mill rollsII and the reel l2 and the efiect of this increased tension is to reducethe gauge of the strip.

After an interval of time sufficient for a point on the strip to passfrom the mill rolls II to the gauge contact rolls 30 has elapsed,conducting segment 39a of the limit switch again rotates into engagementwith the brush 39b and if the increased tension in the strip has notreduced the thickness to within the required tolerance the foregoingoperation is repeated.

If, on the other hand, the increment adjustments of tension weresufiicient to bring the material down to the proper gauge, the mercurycup contacts 34, 36 will be separated and the contactor 42 will notreclose the next time the conducting segment 39a of the limit switch 39rotates into engagement with the stationary bus 39b, and no furtherincrement adjustment in the tension of the strip will be made.

If the strip runs undersize, the movable contact member 34 will makecontact with the lefthand mercury cup contact and this will cause thecontactor 44 and timing relay to function in a manner similar to thatdescribed for contactors 42 and 43, to energize the rheostat motor 4|for rotation in a direction to decrease the amount of resistance in thebias winding of the regulator and thereby to decrease the tension in thestrip between the rolls II and the reel l2. This decreased tension willcause the gauge of the strip to increase, and the operation of thecontactor 44 and the timing relay 45 under the control of the limitswitch 39 and the gauge will This holding circuit The result is that alarger curbe repeated until the thickness of the strip is within therequired tolerance.

During the time that the contactor 42 and its timing relay 43 arefunctioning to increase the tension in the strip the screw loweringcontactor 49 and its time relay 50 are also functioning in a similarmanner. However, this contactor and its relay cannot energize thescrew-down motor 38, unless one of the selector switches 54, 55, 56, isclosed and the conducting segment of one of the corresponding limitswitches 5|, 52, or 53 is in engagement with its cooperating stationarybrush. For example, assume that the switch 55 is selected and closed bythe operator. When the motor operated rheostat 28 has rotated thecontact arm 285, through an arc of in the increase direction, anenergizing circuit for the down contactor 68 will be established fromthe lower bus I4 through the limit switch 52 on selector switch 55,conductor 64, upper contact of contactor 49, operating coil of downcontactor 68 to the upper bus I4. Contactor 68 will close in response toenergization and connect the screw-down motor 38 to the supply sourcefor rotation in a direction to lower the top roll H and thereby todecrease the opening between the rolls. After a predetermined intervalof time determined by the setting of the time delay relay 58, the relay50 functions in a manner similar to the relay 43 to deenergize thecontactor 49 which thereupon opens its contacts to deenergize the coilof the down contactor 58, and contactor 5B in turn opens its contacts todisconnect the screw-down motor 38 from the supply source. If thecorrection so made is insuflicient to restore the thickness of the stripto the required tolerance this action is repeated each time theconducting segment of the limit switch 39 rotates into engagement withthe stationary brush 39b.

If the thickness of the strip should be less than the required tolerancethe contactor 41 and its timing relay 48 will function in a similarmanner to energize the up contactor 65 to close its contacts and connectthe screwdown motor 38 to the source for rotation in a direction toraise the top roll I I toincrease the distance between the rolls. Afteran interval of time determined by the setting of the time delay relay48, the contactors 41 and 65 will be deenergized and the screw-downmotor 38 disconnected from the supply source. It will, of course, beunderstood that the operation of the contactor 41 and its timing relay48 is analogous to that of the contactor 49 and its timing relay 55.That is to say, contactor 41 will not energize the up contactor 65 untilthe tension in the strip has been decreased a predetermined amount andthe limit switch 52 has been rotated through an arc of 90 from theposition in which it is shown in the drawing.

If, on the other hand, selector switch 56 is closed the motor operatedrheostat 28 would have to turn through an arc of either in the tensionincrease or tension decrease direction, before the screw-down motor 38could be energized to raise or lower the rolls.

Thus, means are established for first increasing or decreasing thetension in the strip up to a certain preselectable percentage of thevalue which the tension regulator is set to hold, and

aen lowering or raising the top mill roll in preselectable increments.

At the completion of the rolling of the strip or at the completion of apass, it is desirable to return the motor operated rheostat 28 to itsfirst position so that the basic adjustment of. the tension by the maintension adjusting rheostat 21 is always the same. This is accomplishedby means of limit switches 66 and 51 connected to the shaft of the motoroperated rheostat. It will be noted that as soon as the reel motor isstopped by opening the switch l8, and the consequent opening of the reelmotor line contactor' I1, stationary contacts Ila and lit are bridged bymovable contacts lie and lid respectively, thereby energizing the motord! to rotate in one direction or the other until the insulated segments55a and 61's of the limit switches i6 and. 61 are both in engagementwith their cooperating brushes. When this condition obtains, therheostat motor 3! is brought to rest with the movable rheostat arm 28ain the central position in which it is shown and the limit switches 51,52 and 53 in the positions in which they are. shown in the drawings.

An obvious modification of the scheme shown in Fig. l is to stop theincrement adjustments of tension as soon as the increment adjustments ofthe screwdown are started.

For small variations in gauge, corrections can usually be made byvarying the tension alone. However, upon greater variations it isnecessary to adjust the screws as well as to vary the tension of thestrip. In the modification of Fig. 2, means are provided for makingcorrections in the tension alone when the variations in the gauge arerelatively small, and additional means are provided for simultaneouslyenergizing the screwdown mechanism to raise or lower the. top roll, whenthe variations in the gauge are relatively large, The arrangementdisclosed in the modification of Fig. 2 is substantially identical withthe arrangement disclosed in Fig. 1, but differs from it primarily inthat the contactors and relays which control the screw-down motor arecontrolled by means of a second microammeter l8 supplied from the gaugehead instead of being controlled by a plurality of limit switchesoperated by the rheostat motor cooperating with the indicatingmicroamrneter which controls the tension adjusting mechanism. Thus itwill be noted that that portion of the modification disclosed in Fig. 2of the drawings which is above the dotted line H is identical with acorresponding portion of the modification of Fig; 1. In the portion ofthe modification of'Fig; 2 below the dotted line 7!, limit switchmechanisms corresponding to limit switches Si, 52 and 53 are omitted'andcontactors l2 and 13 corresponding to contactors 41 and d8 of Fig. 1 andtiming relays l4 and 15 corresponding to relays 48 and 50 of Fig. 1 aredirectly controlled from the microammeter 1t supplied from the powerunit in the head of the gauge 15. In addition to a limit switch 1'! forpreventing repeated increment adjustment operation of the tensionadjusting mechanism until a predetermined length of strip 13 has passedthe contact rolls 7% of. the gauge after an increment adjustment hasbeen made, an additional limit switch 88 mounted on the shaft of thelimit switch 7'! is provided for preventing a' repeated actuation of thescrew-down mechanism until a predetermined length of strip has passedthe contact rolls 19 of the gauge after an increment adjustment has beenmade in the position of the top roll 8|.

The contact making microammeter H! is provided with adjustable positionmercury cup contacts 10a and its and with a movable zero center contact1a. Similarly, the contact making iii) microammeter 82 is provided withstationary ad'- justable position mercury cup contacts 82a and 82b andwith a movable contact member 820. The mercury cup contacts 822. and 82bare adjusted so that themovable contact member 820 will make contactwith one or the other of the mercury cup contacts upon small variationsin the gauge of the strip. The gauge 16 then controls the tensionincrement adjustment in a manner identical with that described inconnection with the modification ot Fig. 1. Howeventhe mercury cupcontactslts and 10b of the second contact making microammeter 10 areadjusted so as to make contact on greater variations in gauge. This inturn controls the increment adjusting contactors 8.3 and 8 for thescrew-down motor 85 in a manner similar to that described for thetension increment adjustment.

Thus, if the variation is great, no time is wasted in making severaltension increment adjustments before making an adjustment in thepositionof the top roll. On the contrary, an adjustment of the top roll is madeimmediately and simultaneously with the increment adjustment in tensionof the strip. As' soon as'the large variations have been corrected, thesmall variations will be corrected by tension alone. Otherwise, theoperation of the modified system of Fig. 2 is identical with theoperation of the system of Fig. 1.

The modified system of Fig. 3- is similar to the systems disclosed inFigs. 1 and 2but differs from these systems primarily in thatthe'contact making microammeter 8B is provided with a plurality ofstationary contacts oneach side of the central ero position of themovable contacts 86a. for the purpose of producing increment adjustmentsof the tension of the strips and the position of the top roll 31 morenearly proportional to the amount of adjustment required. Thus, if thevariation in strip thickness is slight, the time setting for theincrement adjustment will be rather short. If the variations stripthickness are somewhat greater, the time setting for the incrementadjustment will be proportionally in- 89 and their timing relays 9i] and9| respectively.

The means for effecting increment adjustments in the position of the toproll 81 comprises con-' tactors 92', 93 and their respective timingrelays 94 and 95. Contactors 88, 89 and 92, 93 correspondin structureand in function with the contactors 42, 44 and 49, 41 respectively ofFig. 1. Similarly, timing relays 90, 9| and 94, 95 correspond withtiming relays 43, 45 and 5t, 48- respectively of Fig. I. The timingrelays 99-, 91 and M, 95 are difierent from the timing relays of Fig. 1,however, in that means are provided for changing the time constants ofthese relays. These means are illustrated as bucking coils 9%, la, 9%and 95's. Additional means are provided for varying the change of thetime'constants of I03, Ill! and H12, and resistances )3, I04, H15

and H36 controlled thereby. The resistanc I03 is divided into threesections I031, I031; and I030 of progressively increasing ohmic values.Similarly, the resistances I04, I05 and I06 are divided intocorrespondingly numbered sections of progressively decreasing ohmicvalue.

Resistances I03, 'I04, I05 and I06 are connected in the circuits ofbucking coils 99a, 94a, 95a. and 9 la respectively.

When the variation in the thickness of the strip from the desiredthickness is suflicient merely to cause the movable contact member 86aof the contact making microammeter to move into engagement withstationary contact 860, an energizing circuit is established for theoperating coil of contactor 91, and this contactor responds to close itsupper main contacts and to open its intermediate and lower contacts. Theupper contacts in closing complete an energizing circuit for theoperating coil of contactor 88 and as a result of this energization,contactor 88 and its timing relay 90 function to energize the rheostatmotor I01 and thereby to change the tension setting of the tensionregulator I08 and to effect an increment adjustment in the tension ofthe strip 96. Simultaneously, the upper contacts of contactor 91complete an energizing circuit for the operating coil of contactor 92and as a result of its energization, this contactor and its cooperatingtiming relay 94 function through contactor I09 to energize thescrew-down motor IIO for rotation in a direction to lower the top roll81.

Intermediate and lower contacts of contactor 91 in opening insertresistance section 3341 in the bucking coil 90a of timing relay 90 andlower contact in opening inserts resistance section 04a,

in the bucking coil 94a of timing relay 94. The result is that the timeconstants of timing relays 90 and 94 are varied to correspond with theamount of variation of the strip thickness from the desired gauge,thereby to produce increment adjustments in the strip tension and in theposition of the top roll 8'! dependent upon the variation.

If the variations of the strip thickness from the desired gauge aresufficiently large to cause the movable contact member 86a of thecontact making microammeter to rotate into engagement with one of thestationary contacts 85c or 86s, the contactor 98 or 99, as the case maybe, will operate to insert resistance sections I03b or I03c in thecircuit of bucking coil 90a, and resistance section I04b or I04c in thecircuit of bucking coil 94a, thereby to vary the time constants of theserelays in accordance with the amount of the variation of the stripthickness from the desired gauge.

If the strip thickness runs less than the desired gauge, the movablecontact member 85a. rotates in the opposite direction to engage thestationary contact members 869, 86: and 86g and thereby to energize oneor the other of contactors I00, IN, or I02. Thesecontactors in turnfunction in a manner similar to that already described for contactors91, 08 and 99, to insert varying amounts of resistance in the buckingcoils 95B and 9's. of timing relays 95 and 9| respectively to change thetime constants of these relays in accordance with the variations in thethickness of the strip from the desired gauge. They also function toenergize contactor 89 which in turn controls the motor I01 to rotate inthe opposite direction thereby to effect a decrease in the setting ofthe regulator I08 and a corresponding increment adjustment in the striptension; and these relays further function to effect energization of thecontactor 92 which acts through contactor II I to produce rotation ofthe screw-down motor H0 in such a direction as to raise the top roll 81.

Throughout the foregoing specification it is to be understood thatincreasing of tension in the strip and reducing the opening between therolls have the same effect; namely, to decrease the gauge of the strip.Decreasing the tension in the strip and increasing the opening betweenthe mill rolls has the opposite effect.

The apparatus of Fig. 4 differs from the apparatus of Figs. 1, 2, and 3primarily in that the means responsive to variations in the thickness ofthe moving material is utilized to control the tension of the materialat a preceding point in its travel instead of at a succeeding point. Inthis modification the invention is shown as embodied in a control systemfor a continuous strip rolling mill having a plurality of elements II 5,H6, and 1 operating on the moving length of material H8. The elements II5 and H6 are illustrated as pairs of rolls for reducing the thicknessof the material H8, and the element II! is illustrated as a take-up reelfor winding the mapractice a continuous rolling mill may have andfrequently does have as many as five or more stands of rollssuccessively operating on a length of moving material.

Dynamo-electric machines H9, I 20, and I2I are mechanically coupled tothe pairs of rolls I I-5 and H6 and to the reel II! respectively. Undernormal operating conditions, the dynamoelectric machines II 9, I20, andI2I operate as motors to drive the reducing rolls H5 and H6 and thetake-up reel III. Under certain operating conditions, one or more ofthese dynamoelectric machines may operate as a generator.

Dynamo-electric machine I2I is supplied from a suitable sourcerepresented by the supply lines I22 to which its armature terminals maybe connected by means of the switching device I23 when the contacts ofthe switching device are closed. Dynamo-electric machines H9 and I20 aresimilarly supplied from a suitable source which may be and preferably isthe same source as that represented by the lines I22.

Suitable current regulating means I24 are provided for maintaining thecurrent input to the motor I2I substantially constant. Regulating meansI24 are identical with regulating means I08 of Fig. 3 with theexceptionthat the bias coil on the movable core member of regulatingmeans I08 is omitted.

Suitable means I25 are provided for measuring variations in thethickness of the material II8 between the rolls H6 and the take-up reelII! and for varying the tension of the material II8 so as to decreasethe variations in thickness. These thickness variation responsive meansare identical with the electric gauge illustrated in Fig. 3, and arepetition of the description of these means is accordingly omitted.

A contact-making microammeter I26 is connected to the output circuit ofthe electric gauge I 25 and this contact-making microammeter controlsthe operation of a pilot motor I21, the shaft of which is connected tothe movable arm of a rheostat I28 connected in the field circuit of'motor I 20. An increment control means I29 is ncluded in the connectionsbetween the microammeter I23 and the motor I21. This increment controlmeans may be substantially the same as the increment control means 88,89, 99, SI of Fig. 3 and for this reason it is shown merelyconventionally in Fig. 4. In the modification of Fig. 3 thecontact-making microammeter 86 is provided with a multiplicity ofcontacts which control contactors 97, 98, 99, I00, NH, and IE2 which inturn control resistors 033,, I031), W3C, I065, I961], Ifific to supplyvariable voltages to the coils 99a, SIa to vary the time setting of thetime element means 90, III of the increment control means. Instead ofthis arrangement, a Variable voltage is obtained from the output circuitof the electric gauge I25 and supplied through a conventional tubeamplifier I313 to the increment control means I29.

The operation is as follows: The regulating means I24 operates tomaintain the current input to the motor I2I substantially constant byincreasing its field strength as the diameter of the coil increases. Asexplained in the foregoing, this results in maintaining the tension inthe material H8 substantially constant between the rolls II 6 and thereel II].

If the thickness of the material II8 becomes greater than the desiredvalue, the gauge means I25 and the contact-making microammeter I26controlled thereby cause the pilot motor I2'I to rotate in such adirection as to rotate the movable arm of the rheostat I28 in aclockwise direction to weaken the field strength of motor I20. Thiscauses the speed of motor I29 to increase which, in turn, increases thetension of the material between the preceding pair of rolls H and therolls I IS. The increasing tension in the material between the rolls H5and H6 decreases the thickness of the material. This operation takesplace by increments the magnitude of which is controlled by theincrement control means I29 in the manner set forth in the descriptionof the operation of the apparatus of Fig. 3.

When the variations in the thickness of the material IIB have beendecreased so that the thickness of the material is again within theallowed tolerances, the gauge means I25 is balanced and the motor I2'Iis deenergized and stopped.

If the thickness of the material becomes less than the desired valuewhich the gauge is set to hold, the motor I21 will be caused to rotatein the reverse direction to strengthen the field of driving motor I20and thereby decrease its speed. This results in decreasing the tensionof the material between the rolls H5 and H6, and this decreasing tensionincreases the thickness of the material. This operation likewise takesplace in a series of increments of a magnitude depending upon themagnitude of the variations in the thickness of the material.

In the modification illustrated in Fig. 5, the apparatus is identicalwith the apparatus shown in Fig. 4 with the exception that a tensiometermechanism I SI responsive to variations in the tension of the materialI32 between the pair of rolls I33 and the preceding pair of rolls I35 isprovided for controlling the driving motor I35 for the rolls I33 todecrease the variations in tension and thereby to maintain the tensionsubstantially constant. This tensiometer mechanism I3! does not directlycontrol the excitation of motor I35 but on the contrary, controls theexcitation of a buck-boost exciter I36, th'e armature of which isconnected in the field circuit of motor I35.

III

The structural details of the tensiometer mechanism I3I and itsoperation are fully described in United States Patent No. 2,100,653, L.A. Umansky, dated November 30, 1937, and a detailed description isaccordingly omitted from this specification. It is sufficient tounderstand that the tensiometer mechanism is provided with means I3?illustrated as a, calibrated rheostat for setting the value of thetension that it is desired'to hold in the material, and that thetensiometer controls the buck-boost exciter I36 to vary the excitationof motor I so as to maintain the tension of the material I32substantially constant at the value set upon the calibrated rheostat.This calibrated rheostat corresponds in structure and in function to thecalibrated rheostat 33 shown in the Umansky patent. As shown, it isprovided with a movable contact arm IB'Ia which is connected to theshaft of the motor I38. Since the remainder of the apparatus isidentical with that of Fig. 4, it will be clear that if the thickness ofthe material I32 between the rolls I33 and the reel I39 becomes greaterthan the value the gauge I4!) is set to hold, the motor I38 will rotatein a direction, e. g. the clockwise direction, to increase the-tensionsetting of the tensiometer I3I. The tensiometer I3I operates through thebuck-boost exciter I36 to weaken the field strength of the motor I35 andthereby increase its speed and that of the rolls I33 driven thereby.This increased speed increases the tension of the material between rollsI33 and the preceding pair of rolls I34 and thereby decreases thethickness of the material, This operation of increasing the tension ofthe material I32 takes place in a series of increments under the controlof the increment control mechanism MI and as explained in thedescription of Figs. 3 and 4, the magnitude of these increments isproportional to the magnitude of the variations in the thickness of thematerial from the set value.

If the thickness of the material becomes less than the value the gauge Iis set to hold, the motor I38 will rotate in the reverse direction andas a result the tension of the material I32 between the pairs of rollsI33 and I34 will be decreased in a series of increments of variablemagnitude. The remaining features of the operation are identical withcorresponding features explained in the description of Fig. 4.

Although in accordance with the provisions of the patent statutes thisinvention is described as embodied in concrete form, it will beunderstood that the specific elements, apparatus and their arrangementand connection in the various modifications are merely illustrative andthat the invention is not limited thereto, since alterations andmodifications will readily suggest themselves to persons skilled in theart without departing from the true spirit of this invention or from thescope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A control system for rolling mills and the like having a pair ofrolls for reducing the thickness of a length of moving material and areel for the material comprising in combination, a dynamo-electricmachine mechanically coupled to drive said rolls, a seconddynamoelectric machine mechanically coupled to said reel, and meansresponsive to variations in the thickness of said material forcontrolling the excitation of one of said machines to vary the tensionof said material so as to decrease the variations in thickness of saidmaterial.

2. A control system for rolling mill apparatus and the like having apair of rolls for reducing the thickness of a length of moving material,a reel for said material and separate dynamoelectric machinesmechanically coupled to said rolls and said reel comprising incombination, a regulator for maintaining the current input to one ofsaid machines and the tension of said material substantially constant,and gauging means responsive to variations in the thickness of saidmaterial for varying the setting of said regulator thereby to vary thetension of said material so as to decrease the variations in thicknessof the material.

3. A control system for rolling mill apparatus and the like having anelement operating on a length of moving material and a dynamo-electricmachine mechanically coupled to said element comprising in combination,means responsive to variations in the thickness of said material forcontrolling said dynamo-electric machine to vary the tension of saidmaterial by increments to decrease the variations in thickness of saidmaterial, and means responsive to the magnitude of said thicknessvariations for controlling the magnitude of said increments.

4. A control system for rolling mill apparatus and the like having anelement operating on a length of moving material and. an electric motormechanically coupled to said element comprising in combination, anelectric gauge responsive to variations in the thickness of saidmaterial and means controlled thereby for varying the speed of saidmotor to vary the tension of the material by increments so as todecrease the variations in thickness of the material, and meanscontrolled by said gauge for varying the magnitude of said increments inproportion to the magnitude of said thickness variations.

'5. A control system for material modifying apparatus or the like havinga pair of elements operating successively on a length of material andindividual dynamo-electric machines mechanically coupled to saidelements comprising in combination, a current regulator for maintainingthe armature current of one of said machines substantially constant, andmeans responsive to variations in the thickness of said material forcontrolling the other of said dynamo-electric machines to vary thetension of said material to decrease the thickness variations of saidmaterial.

6. A control system for rolling mill apparatus and the like having aplurality of elements for successively operating on a length of movingmaterial, and an electric motor for driving one of said elements and asecond electric motor for driving another of said elements comprising incombination, a current regulator for maintaining the current input toone of said motors substantially constant, and means responsive tovariations in the thickness of said material for controlling the speedof the other of said motors to vary the tension of said material todecrease the thickness variations of said material.

'7. A control system for rolling mill apparatus and the like having anelement operating on a lengthof moving material and a dynamo-electricmachine mechanically coupled to said element comprising in combination,an electric gauge responsive to variations in 'the thickness of saidmaterial for producing control voltages proportional to said variations,means responsive to said voltage for controlling said machine to varythe tension of said material by increments to decrease the variations inthickness of said material, and means responsive to said voltages forvarying the amount of said increments in proportion to the amount ofsaid thickness variations.

FRANCIS MOHLER.

